CLEANUP: config: provide cleare hints about unsupported QUIC addresses

We now detect that QUIC was likely requested, and if it's not compiled
it, we clearly mention it.
diff --git a/src/tools.c b/src/tools.c
index 71337aa..9e629e5 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -1300,11 +1300,18 @@
 					    ctrl_type == SOCK_DGRAM);
 
 		if (!new_proto && (!fqdn || !*fqdn) && (ss.ss_family != AF_CUST_EXISTING_FD)) {
-			memprintf(err, "unsupported %s protocol for %s family %d address '%s'",
+			memprintf(err, "unsupported %s protocol for %s family %d address '%s'%s",
 				  (ctrl_type == SOCK_DGRAM) ? "datagram" : "stream",
 				  (proto_type == PROTO_TYPE_DGRAM) ? "datagram" : "stream",
 				  ss.ss_family,
-				  str);
+				  str,
+				  (ctrl_type == SOCK_STREAM && proto_type == PROTO_TYPE_DGRAM) ?
+#ifndef USE_QUIC
+				  "; QUIC is not compiled in if this is what you were looking for."
+#else
+				  ""
+#endif
+				  :"");
 			goto out;
 		}